The present invention relates to a developer-carrying member, a developing apparatus and an image forming apparatus used for a copying machine, a laser beam printer, a facsimile apparatus, a printing apparatus, etc., according to electrophotography.
Hitherto, a developer-carrying member has been provided with a roughened uneven surface for conveying the developer. As old examples, Japanese Laid-Open Patent Application (JP-A) 54-79043 has disclosed one provided with knurled grooves or ridges for principally the two-component developing scheme, and JP-A 55-26526 has disclosed one provided with a roughened surface for principally the mono-component developing scheme.
Particularly, for providing a developer-carrying member having a roughened surface, it has been proposed to coat a substrate with a surface-coating layer of a relatively high hardness material for preventing the wearing of surface unevennesses during long-term use. For example, JP-A 58-132768 has disclosed a developer-carrying member comprising an aluminum substrate surface-coated with a layer of a nitride such as TiN or CrN, a carbide such as TiC or B4C, or Nixe2x80x94P plating; JP-A 6-230676 has disclosed a developer-carrying member comprising a substrate of aluminum, brass or stainless steel surface-coated with Cr plating, anodized aluminum film layer, Nixe2x80x94P plating or nitriding layer; and JP-A 3-41485 has disclosed a developer-carrying member comprising a substrate of aluminum, stainless steel, etc., surface-coated with a plating layer of Cr, Cuxe2x80x94Cr, Nixe2x80x94Cr, Cuxe2x80x94Nixe2x80x94Cr, Nixe2x80x94Cuxe2x80x94Nixe2x80x94Ca, etc.
Such known wear-resistant surface coating layers include a highly wear-resistant layer, such as an electroless Nixe2x80x94P plating layer which can be provided with a Vickers hardness of 900 or higher through a heat treatment at 300-500xc2x0 C. (JP-A 58-132768). However, such a heat treatment results in a substantial lowering in satisfactory product yield. This is because the substrate causes a thermal deformation of several tens of xcexcm or larger in a direction vertical to the extension direction thereof, so that the spacing between the electrostatic image-bearing member and the developer-carrying member is locally fluctuated to cause image irregularity in the product toner image. Such an image irregularity seriously obstructs high-quality toner image formation.
A surface-coating layer formed by electroplating is rigid and excellent in wear resistance, and is moreover advantageous that it does not require a high-temperature heating treatment.
However, the formation of a surface-coating layer by electroplating is also accompanied with a difficulty as follows. In the electroplating, a metal is precipitated from a plating solution and deposited on a substrate in proportion to a density of lines of electric force, but a substrate surface is generally accompanied with minute projections and cracks. The lines of electric force tend to be concentrated toward the top of each projection or the edges of each crack. Accordingly, the metal is abnormally deposited at such sites, thus making it difficult to provide a rigid plating layer having a prescribed surface roughness. For overcoming such a difficulty, JP-A 2000-284586 has proposed a developer-carrying member which has been formed by first forming an electroless plating intermediate layer on a substrate, and forming successively thereon an Ni joint layer and a rigid electroplating layer.
In recent years, along with a desire for a higher-speed image forming apparatus, it has been demanded to achieve a higher-speed image formation while retaining a basic apparatus organization. In case where a developer-carrying member having a laminate structure as described above is incorporated in such a high-speed image forming apparatus, there has been observed a phenomenon that when an objective image like a lateral line as shown in FIG. 3A is reproduced, the resultant image is accompanied with trailing ears as shown in FIG. 3B. The phenomenon may be referred to as xe2x80x9ctailing (of images)xe2x80x9d hereinafter.
Accordingly, an object of the present invention is to provide a developer-carrying member capable of providing images free from such tailing even when incorporated in a high-speed image forming apparatus.
Further objects of the present invention are to provide a developing apparatus and an image forming apparatus using such a developer-carrying member and capable of forming good toner images.
According to the present invention, there is provided a developer-carrying member for carrying and conveying thereon a developer, having a laminate structure including successively a substrate having a surface roughness, an intermediate layer having a surface roughness smaller than that of the substrate, a joint layer and an electroplating layer, wherein the joint layer comprises a material having a volume susceptibility of at most 1.
As used herein, the term xe2x80x9csusceptibilityxe2x80x9d of a material means susceptibility per unit mass ("khgr") expressed in centimeter, gram, second (CGS) electromagnetic units, multiplied by 106, i.e., susceptibility equals "khgr" x 106 CGS.
The present invention also provides:
a developing apparatus for developing an electrostatic latent image formed on an image-bearing member, the developing apparatus comprising a developer-carrying member which has a laminate structure including successively a substrate having a surface roughness, an intermediate layer having a surface roughness smaller than that of the substrate, the above-mentioned joint layer and an electroplating layer; and
an image forming apparatus, comprising: an image-bearing member for forming thereon an electrostatic image thereon, and a developer-carrying member disposed opposite to the image-bearing member for carrying and conveying thereon to develop the electrostatic image, wherein the developer-carrying member has a laminate structure including successively a substrate having a surface roughness, an intermediate layer having a surface roughness smaller than that of the substrate, the above-mentioned joint layer and an electroplating layer.
The developer-carrying member of the present invention includes an intermediate layer and a rigid electroplating layer, between which is disposed a joint layer for increasing the adhesion between the two layers comprising a material which has a susceptibility of at most 1 CGS, i.e., is substantially non-magnetic. As a result, the problem of tailing can be solved. In the case of a conventional Ni plating joint layer, Ni is a ferromagnetic material having a susceptibility of 49000 CGS, which is considered to cause the tailing. More specifically, because of the ferro-magnetism, the Ni plating joint layer affects the shapes of toner ears on the developer-carrying member surface, and long toner ears are caused to be transferred onto the electrostatic image-bearing member, thus causing the tailing of images. The tailing becomes more noticeable at a higher image forming speed. This is considered to be because the toner receives a larger mechanical stress and a larger heat of friction in proximity to the developer-carrying member surface at a higher image forming speed, so that the toner is liable to be agglomerated.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.